U.S. patent application number 13/700263 was filed with the patent office on 2013-08-22 for method for the preparation of a particulate reversibly crosslinked polymeric material.
This patent application is currently assigned to Dow Global Technologies LLC. The applicant listed for this patent is Purnendu Mukherjee, Eric P. Wasserman. Invention is credited to Purnendu Mukherjee, Eric P. Wasserman.
Application Number | 20130217873 13/700263 |
Document ID | / |
Family ID | 42352011 |
Filed Date | 2013-08-22 |
United States Patent
Application |
20130217873 |
Kind Code |
A1 |
Mukherjee; Purnendu ; et
al. |
August 22, 2013 |
METHOD FOR THE PREPARATION OF A PARTICULATE REVERSIBLY CROSSLINKED
POLYMERIC MATERIAL
Abstract
The present invention relates to method for the preparation of a
particulate reversibly-crosslinked polymeric material comprising:
treating a particulate water-soluble hydroxyl-functional polymer in
a liquid phase comprising a solvent mixture in that the
hydroxyl-functional polymer is insoluble containing an organic
solvent and water; a tetracarboxylic acid dianhydride represented
by formula (I), 10 (I) wherein: U and V are independently selected
from CH, N and P; 15 X is selected from a single bond, a saturated
divalent (C.sub.1-C.sub.10) hydrocarbon group, O, S, NR, and PR,
wherein R is selected from hydrogen and (C.sub.1-C.sub.4) alkyl; n
and m are independently selected from 0 and 1; w is 1 or 2 with the
proviso that; 20 if w is 1 then Y is X and if w is 2 then Y is
selected from H and (C.sub.1-C.sub.4) alkyl, whereby there is no
bond between both Y; and optionally a catalyst; to form a
particulate reversibly-crosslinked polymeric material and 25 to a
particulate reversibly-crosslinked polymeric material obtainable
thereby. ##STR00001##
Inventors: |
Mukherjee; Purnendu;
(Piscataway, NJ) ; Wasserman; Eric P.; (Hopewell,
NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mukherjee; Purnendu
Wasserman; Eric P. |
Piscataway
Hopewell |
NJ
NJ |
US
US |
|
|
Assignee: |
Dow Global Technologies LLC
Midland
MI
|
Family ID: |
42352011 |
Appl. No.: |
13/700263 |
Filed: |
June 8, 2010 |
PCT Filed: |
June 8, 2010 |
PCT NO: |
PCT/IB2010/001388 |
371 Date: |
December 10, 2012 |
Current U.S.
Class: |
536/63 |
Current CPC
Class: |
C08B 15/005 20130101;
C08B 3/10 20130101 |
Class at
Publication: |
536/63 |
International
Class: |
C08B 3/10 20060101
C08B003/10 |
Claims
1. A method for the preparation of a particulate
reversibly-crosslinked polymeric material comprising: treating a
particulate water-soluble hydroxyl-functional polymer in a liquid
phase comprising a solvent mixture in that the hydroxyl-functional
polymer is insoluble comprising an organic solvent and water; and a
tetracarboxylic acid dianhydride represented by formula (I),
##STR00004## wherein: U and V are independently selected from CH, N
and P; X is selected from a single bond, a saturated divalent
(C.sub.1-C.sub.10) hydrocarbon group, O, S, NR, and PR, wherein R
is selected from hydrogen and (C.sub.1-C.sub.4) alkyl; n and m are
independently selected from 0 and 1; w is 1 or 2 with the proviso
that; if w is 1 then Y is X and if w is 2 then Y is selected from H
and (C.sub.1-C.sub.4) alkyl, whereby there is no bond between both
Y; to form a particulate reversibly-crosslinked polymeric
material.
2. The method of claim 1, comprising a) suspending and maintaining
the particulate water-soluble hydroxyl-functional polymer in the
liquid phase to form the particulate reversibly-crosslinked
polymeric material; and b) separating the particulate
reversibly-crosslinked polymeric material from the liquid
phase.
3. The method of claim 1, wherein the solvent mixture comprises
water in an amount of 2 to 50 weight %, based on the total weight
of the solvent mixture.
4. The method of claim 1, wherein the organic solvent is selected
from acetone, 2-propanol, t-butanol, ethanol, tetrahydrofuran,
2-butanone and ethylacetate.
5. The method of claim 1, wherein the tetracarboxylic acid
dianhydride is present in the liquid phase in an amount of
10-50,000 wppm based on the total weight of hydroxyl-functional
polymer.
6. The method of claim 16, wherein the catalyst is present in
amounts of 0.001 to 10 mol % based on the total moles of anhydride
groups.
7. The method of claim 1, wherein the liquid phase additionally
comprises a catalyst selected from metal alkoxides, metal
carboxylates, Bronsted acids and Lewis bases.
8. The method of claim 7, wherein the catalyst is imidazole.
9. The method of claim 1, whereby in formula (I) U and V are
independently selected from CH and N; X is selected from a single
bond and a saturated divalent (C.sub.1-C.sub.4) hydrocarbon group
and if w is 2 then Y is H.
10. The method of claim 1, wherein the tetracarboxylic acid
dianhydride is selected from 1,2,3,4-butanetetracarboxylic acid
dianhydride; ethylenediaminetetraacetic acid dianhydride; and
1,2,3,4-cyclopentanetetracarboxylic acid dianhydride.
11. The method of claim 1, wherein the hydroxyl-functional polymer
is selected from cellulose derivatives; acrylic polyols; polyester
polyols; polyurethane polyols; polyvinyl alcohol; starch, starch
derivatives; guar and xanthan gums.
12. The method of claim 1, wherein the hydroxyl-functional polymer
is selected from hydroxyethyl cellulose, hydroxypropyl cellulose,
methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl
methyl cellulose, carboxy methyl cellulose and derivatives
thereof.
13. The method of claim 1, wherein the hydroxyl-functional polymer
is cationically-modified hydroxyethyl cellulose.
14. The method of claim 1, wherein the particulate water-soluble
hydroxyl-functional polymer is present in amount of 1-50 weight %
based on the total weight of the liquid phase.
15. A particulate reversibly crosslinked polymeric material
obtainable by the process of claim 1.
16. The method of claim 1 wherein the liquid phase additionally
comprises a catalyst.
17. The method of claim 1 wherein the method additionally comprises
the steps of washing and drying the particulate
reversibly-crosslinked polymeric material.
Description
[0001] The present invention relates to a method for the
preparation of a particulate reversibly-crosslinked polymeric
material and to a particulate crosslinked polymeric material
obtainable by such method.
BACKGROUND OF THE PRESENT INVENTION
[0002] Some water-soluble polymers such as cellulose ethers are
difficult to dissolve in water due to the fact that the first
particles that come into contact with water immediately swell and
stick to each other, forming a gel-like barrier that shields the
remaining polymers from hydration. These water-soluble polymers are
conveniently supplied as a particulate dry material that is then
dissolved in water for the desired end use of such water-soluble
polymers. The above-described gel-blocking behavior of
water-soluble polymers is a considerable drawback for those
applications of water-soluble polymers that comprise the solution
of the particulate water-soluble polymer such as cellulose ethers
in aqueous systems.
[0003] One approach used in industry to overcome this problem, if
permissible in the end-use application, is to apply glyoxal to the
cellulose ether to form a hydrolytically-unstable network. The
crosslinking of the cellulose ether with glyoxal is therefore
reversible in aqueous medium and thus treated cellulose ether can
be suspended in aqueous medium and ultimately dissolved when the
crosslinked network formed with glyoxal is hydrolytically cleaved.
The drawback of this method is that glyoxal is considered as a
toxic compound and is regenerated upon hydrolysis of the
crosslinked network. Thus, alternatives avoiding the
above-described gel-blocking behavior are desired.
[0004] U.S. Pat. No. 3,362,847 discloses a process for improving
the water-dispersibility of water-soluble cellulose ether by
treating the surface of the particulate cellulose ether with a
combination of a water-soluble polybasic organic carboxylic acid
having from 2 to 10 carbon atoms and a water-soluble organic
polyamine having at least two primary amino groups. Preferably, the
polybasic acid and amine are applied to the cellulose ether by
dissolving the polybasic organic carboxylic acid and the
water-soluble organic polyamine in a solvent, which is a
non-solvent for the cellulose ether, and suspending the cellulose
ether in such treating solution.
[0005] U.S. Pat. No. 3,461,115 relates to a process for the
preparation of a macromolecular compound containing hydroxyl
groups, which is soluble in water without forming lumps. This
process comprises treating the water-soluble macromolecular
compound in the solid state with 0.5 to 5% by weight of an
aliphatic dicarboxylic acid containing 2 to 8 carbon atoms, or a
salt or an ester thereof.
[0006] GB 1,017,746 describes a method of producing a crosslinked
product from cellulose or a cellulose derivative, which comprises
reacting a solution or suspension of the cellulose or cellulose
derivative in an organic liquid with the anhydride of a tetra- or
higher basic carboxylic acid in the presence of an organic is base
containing nitrogen. This method allows preparing clear and
transparent products in a simple way. According to the examples the
cellulose derivative is dissolved in an organic solvent such as
acetone and the crosslinking reaction results in a stiff, more or
less transparent gel. This reference neither discloses the
preparation of a water-soluble particulate polymeric material nor
addresses the problem of gel-blocking when dissolving such a
polymeric material.
[0007] US 2005/0143572 relates to a method for the production for
cellulose ethers whereby the cellulose ethers having free hydroxyl
groups are reacted with dicarboxylic and/or polycarboxylic acids
and a nitrogen-containing compound. The process comprises
intensively mixing essentially dry, pulverulent cellulose ether
with a mixture of organic bifunctional and/or polyfunctional acid
and nitrogen-containing compound in a non-nucleophilic organic
solvent prior to reacting the cellulose ether to provide the
modified cellulose ether, which can be stirred into water at a pH
greater than or equal to 11 without agglutination.
[0008] The object of the present invention is to provide a process
for the preparation of a particulate reversibly crosslinked
polymeric material that can be effectively performed under mild
conditions that result in delay of the dissolution of the
water-soluble polymer in an aqueous system even at lower
crosslinker levels. Another goal of the present invention is to
avoid formation of by-products upon dissolution of the
water-soluble polymers that may cause a health concern so that the
products of the present invention can also be used in food,
personal care or pharmaceutical applications.
SUMMARY OF THE INVENTION
[0009] This and other objects as will be discussed below have been
attained by a method for the preparation of a particulate
reversibly crosslinked polymeric material comprising:
treating a particulate water-soluble hydroxyl-functional polymer in
a liquid phase comprising [0010] a solvent mixture in that the
hydroxyl-functional polymer is insoluble comprising an organic
solvent and water; [0011] a tetracarboxylic acid dianhydride
represented by formula (I),
[0011] ##STR00002## [0012] wherein: [0013] U and V are
independently selected from CH, N and P; [0014] X is selected from
a single bond, a saturated divalent (C.sub.1-C.sub.10) hydrocarbon
group, O, S, NR, and PR, wherein R is selected from hydrogen and
(C.sub.1-C.sub.4) alkyl; [0015] n and m are independently selected
from 0 and 1; [0016] w is 1 or 2 with the proviso that; [0017] if w
is 1 then Y is X and [0018] if w is 2 then Y is selected from H and
(C.sub.1-C.sub.4) alkyl, whereby there is no bond between both Y;
and [0019] optionally a catalyst; to form a particulate reversibly
crosslinked polymeric material and by a particulate crosslinked
polymeric material obtainable by such method.
[0020] The present inventors have surprisingly discovered that
particulate water-soluble hydroxyl-functional polymers, especially
cellulose derivatives like cellulose ether can be effectively
crosslinked using a tetracarboxylic acid dianhydride represented by
formula I as defined above under mild conditions when suspended in
a water-containing solvent mixture in which the polymer is
insoluble. This result was very surprising since a person skilled
in the art would expect that carboxylic acid anhydrides would react
in an aqueous medium to form the corresponding carboxylic acids,
which have been proven considerably less effective compared to the
tetracarboxylic acid dianhydrides according to the present
invention.
[0021] Furthermore, it is a surprising result of the present
invention that the method can be run under very mild reaction
conditions, especially ambient conditions even without any
catalysts like amines as taught in the above-discussed prior art.
Thus, according to one aspect of the present invention the method
is performed without the presence of amines or even without any
kind of catalysts.
[0022] The crosslinked particulate hydroxyl-functional
water-soluble polymer obtainable by the process of the present
invention has significant advantages compared to prior art
products. In contrary to the glyoxal-crosslinked material as used
in the prior art no harmful compounds like glyoxal are released
when dissolving the crosslinked particulate polymeric material of
the present invention. The primary product that is released upon
dissolution of the polymers according to the present invention is a
tetracarboxylic acid, which is considered less harmful compared to
glyoxal. Furthermore, a sufficient delay of dissolution of the
particulate water-soluble polymer can be achieved at low
crosslinker level and the dissolution rate can be tailored as a
function of the relative amount of a tetracarboxylic anhydride.
[0023] Furthermore, the present method is applicable to a large
number of hydroxyl-functional water-soluble polymers. Suitable
hydroxyl-functional polymers to be employed in the present
invention are cellulose derivatives, especially cellulose ethers,
hydroxyl-functional acrylate polymers, polyvinyl alcohols,
water-soluble polysaccharides, particularly starch and guar as well
as xanthan gums. According to one aspect of the present invention
the water-soluble hydroxyl-functional polymer is a cellulose
derivative, whereby cellulose ethers are particularly
preferred.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0024] According to the method of the present invention the
particulate water-soluble hydroxyl-functional polymer is treated in
a liquid phase comprising a solvent mixture in which the
hydroxyl-functional polymer is insoluble containing an organic
solvent and water, and a tetracarboxylic acid dianhydride
represented by formula I as defined above. The selection of the
organic solvent is not practically critical as long as the solvent
in its mixture with water in a particular ratio results in a liquid
phase in that the hydroxyl-functional water-soluble polymer is
insoluble to obtain a suspension of the polymer in the liquid
medium. It is preferred to use organic solvents that are, at least
within the employed ratio of solvent to water, miscible with water
in order to form a homogeneous continuous phase for the dispersion.
Furthermore, of course, the organic solvent should not
substantially react with the tetracarboxylic acid anhydride under
the reaction conditions employed. It is also possible to use a
mixture of two and more organic solvents as long as the above
requirements are fulfilled. A suitable solvent may be selected from
at least partially water-miscible aprotic solvents or lower
alcohols, especially C.sub.2 to C.sub.4 alcohols. Suitable aprotic
solvents are ketones, cyclic or acyclic ethers, esters and dimethyl
sulfoxide. Suitable C.sub.2 to C.sub.4 alcohols are ethanol,
2-propanol, 1-butanol, 2-butanol, t-butanol. Suitable ketones are
acetone and 2-butanone, a suitable ether is tetrahydrofuran and a
suitable ester is ethyl acetate. During the preparation of the
crosslinked particles, it is desired that the particles do not
stick to each other or dissolve to any significant extent. If the
particles stick to each other, the final product may consist of
large lumps that would be difficult to re-hydrate after drying.
Also, because this reaction is most efficiently conducted at
relatively high solids contents (>5%), the dissolution of a
substantial fraction of the polymer starting material would render
the mixture extremely viscous and difficult to agitate and convey.
Thus the organic/water mixture in which the polymer is suspended
should not allow more than about 10, no more than 9, no more than
8, no more than 7, no more than 6, no more than 5, no more than 4,
no more than 3, no more than 2, or no more than 1 wt.-% of the
polymer to dissolve. It is preferred that the solvent mixture does
not cause the particles to fuse into a mass if agitation ceases for
up to 15 minutes.
[0025] The amount of water in the solvent mixture can be varied
within wide ranges as long as, depending on the organic solvent or
mixture of organic solvents employed and the type of
hydroxyl-functional water-soluble polymer, the requirement that the
polymer is substantially insoluble in the solvent mixture is
achieved. The lower limit for the amount of water can be as low as
1 weight % of water based on the total weight of the solvent
mixture. Other suitable lower limits of water in the solvent
mixture are 2 weight %, 3 weight %, 4 weight %, 5 weight %, 6
weight %, 7 weight %, 8 weight %, 9 weight %, 10 weight %, 11
weight %, 12 weight %, 13 weight %, 14 weight %, 15 weight %, 16
weight %, 17 weight %, 18 weight %, 19 weight %, 20 weight % based
on the total weight of the solvent mixture depending on the type of
hydroxyl-functional water-soluble polymer and the one or more
organic solvents to be used in the solvent mixture; the upper limit
of the water content may be as high as 60 weight % based on the
total weight of the solvent mixture. Other suitable upper limits
are 55 weight %, 50 weight %, 45 weight %, 40 weight %, 35 weight
%, 30 weight %, 25 weight %, 24 weight %, 23 weight %, 22 weight %,
21 weight %, 20 weight %, 21 weight %, 20 weight %, 19 weight %, 18
weight %, 17 weight %, 16 weight %, 15 weight %, 14 weight %, 13
weight %, 12 weight %, 11 weight %, or 10 weight % based on the
total weight of the solvent mixture.
[0026] Without wanting to be bound by theory, it is believed that
the water present in the solvent mixture according to the method of
the present invention activates the hydroxyl-functional
water-soluble polymers and allows the penetration of the
tetracarboxylic acid dianhydride into the polymer particles below
the surface. It was surprisingly found, in contrast to the
expectations, that the water does not deactivate the
tetracarboxylic acid dianhydride but on the contrary has a positive
effect on process efficiency and also on product properties.
Especially the crosslinking efficiency of very low levels of
crosslinker may be attributed to the penetration of the crosslinker
into outer areas of the polymer particles with the result that not
only surface crosslinking but also crosslinking underneath the
surface layer of the polymer particle occurs
[0027] The water-soluble polymeric polyol may have a solubility in
water of at least 1 g, more preferably at least 3 g, most
preferably at least 5 g in 100 g of distilled water at 25.degree.
C. and 101325 Pa (1 atm).
[0028] The water-soluble polymeric polyol is preferably selected
from one or more polysaccharides, homo- and copolymers comprising
in polymerized form an unsaturated alcohol such as 2-hydroxyethyl
acrylate or a vinyl alcohol.
[0029] The water-soluble polymeric polyol generally has a weight
average molecular weight of at least 10,000, preferably at least
12,000, more preferably at least 15,000, most preferably at least
18,000. The preferred upper limit for the weight average molecular
weight largely depends on the type of polymer. Generally the weight
average molecular weight of the water-soluble polymer is up to
10,000,000, preferably up to 8,000,000, more preferably up to
5,000,000. The weight average molecular weight is determined by
light scattering according to the Standard Test Method ASTM
D-4001-93 (2006).
[0030] One preferred type of water-soluble polymer a) is a
polysaccharide. Examples of polysaccharides include gum arabic,
xanthan gum, gum karaya, gum tragacanth, gum ghatti, carrageenan,
dextran, alginates, agar, gellan gum, gallactomannans such as guar
and locust bean gums, pectins, starches, starch derivatives, guar
derivatives, xanthan derivatives, and cellulose derivatives. Starch
derivatives, guar derivatives and xanthan derivatives are described
in more detail in European patent EP 0 504 870 B, page 3, lines
25-56 and page 4, lines 1-30. Useful starch derivatives are for
example starch ethers, such as hydroxypropyl starch or
carboxymethyl starch. Useful guar derivatives are for example
carboxymethyl guar, hydroxypropyl guar, carboxymethyl hydroxypropyl
guar or cationized guar.
[0031] Preferred hydroxypropyl guars and the production thereof are
described in U.S. Pat. No. 4,645,812, columns 4-6. Preferred
polysaccharides are cellulose esters or cellulose ethers. Preferred
cellulose ethers are carboxy-C.sub.1-C.sub.3-alkyl celluloses, such
as carboxymethyl celluloses; carboxy-C.sub.1-C.sub.3-alkyl
hydroxy-C.sub.1-C.sub.3-alkyl celluloses, such as carboxymethyl
hydroxyethyl celluloses; C.sub.1-C.sub.3-alkyl celluloses, such as
methylcelluloses; C.sub.1-C.sub.3-alkyl hydroxy-C.sub.1-3-alkyl
celluloses, such as hydroxyethyl methylcelluloses, hydroxypropyl
methylcelluloses or ethyl hydroxyethyl celluloses;
hydroxy-C.sub.1-3-alkyl celluloses, such as hydroxyethyl celluloses
or hydroxypropyl celluloses; mixed hydroxy-C.sub.1-C.sub.3-alkyl
celluloses, such as hydroxyethyl hydroxypropyl celluloses, or
alkoxy hydroxyethyl hydroxypropyl celluloses, the alkoxy group
being straight-chain or branched and containing 2 to 8 carbon
atoms. Most preferably, the composition comprises a water-soluble
cellulose ether, such as a methylcellulose with a degree of methyl
substitution DS.sub.methoxyl of from 1.2 to 2.2, preferably from
1.5 to 2.0, or a hydroxypropyl methylcellulose with a
DS.sub.methoxyl of from 0.9 to 2.2, preferably from 1.1 to 2.0 and
a MS.sub.hydroxypropoxyl of from 0.02 to 2.0, preferably from 0.1
to 1.2. Generally the weight average molecular weight of the
polysaccharide is up to 20,000,000, preferably up to 5,000,000,
more preferably up to 1,000,000.
[0032] More preferably, the water-soluble polymer is an
above-described cellulose ether. Most preferably, the water-soluble
polymer is hydroxyethyl cellulose, cationic hydroxyethyl cellulose,
hydroxypropyl methyl cellulose, or methyl cellulose.
[0033] One advantage of the process of the present invention is
that due to be insolubility of the water-soluble
hydroxyl-functional polymer in the solvent mixture relatively high
concentrations of a polymer in the liquid phase can be used in the
method according to the present invention. Water-soluble
hydroxyl-functional polymers, especially cellulose ethers
substantially increase the viscosity of the solution even at very
low concentrations. Since according to the present invention the
solvent mixture is selected to avoid an appreciable dissolution of
the polymer in the liquid phase the substantial increase of the
viscosity can be avoided even at very high concentration of the
hydroxyl-functional water-soluble polymer. Thus the method of the
present invention can still be run efficiently at an amount of
particulate water-soluble hydroxyl-functional polymer of as high as
50 weight % based on the total weight of the liquid phase. Suitable
upper limits for the amount of the polymer are 45 weight %, 35
weight %, 30 weight %, 25 weight %, or 20 weight % of polymer based
on the total weight of the liquid phase. Suitable lower limits for
the amount of water-soluble hydroxyl-functional polymer are 1
weight %, 5 weight %, 7 weight %, 10 weight % or 15 weight % based
on the total weight of the liquid phase.
[0034] The tetracarboxylic acid dianhydrides according to the
present invention are represented by formula I:
##STR00003##
wherein: [0035] U and V are independently selected from CH, N and
P; [0036] X is selected from a single bond, a saturated divalent
(C.sub.1-C.sub.10) hydrocarbon group, O, S, NR, and PR, wherein R
is selected from hydrogen and (C.sub.1-C.sub.4) alkyl; [0037] n and
m are independently selected from 0 and 1; [0038] w is 1 or 2 with
the proviso that; [0039] if w is 1 then Y is X and [0040] if w is 2
then Y is selected from H and (C.sub.1-C.sub.4) alkyl, whereby
there is no bond between both Y.
[0041] Suitable compounds to be used in accordance of the present
invention are represented by formula I wherein U and V are
independently selected from CH and N, particularly U and V are CH,
X is independently selected from a single bond and a saturated
divalent (C.sub.1 to C.sub.4) hydrocarbon group and if w is 2 then
Y is H. Particularly suitable tetracarboxylic acid dianhydrides are
selected from 1,2,3,4-butanetetracarboxylic acid dianhydride,
ethylenediaminetetraacetic acid dianhydride and
1,2,3,4-cyclopentanetetracarboxylic acid dianhydride.
[0042] As discussed above one advantage of using the
tetracarboxylic acid dianhydrides according to the present
invention as crosslinkers is that these crosslinkers are very
effective already at low levels, and that the dissolution behavior
of the reversibly crosslinked polymeric material according to the
present invention can be easily tailored by selecting the
appropriate level of the crosslinkers. Thus, the amount of such
tetracarboxylic acid dianhydride can be varied with in wide ranges.
A lower limit for the amount of tetracarboxylic acid dianhydride is
10 wppm, 50 wppm, 100 wppm, 150 wppm, 200 wppm, 250 wppm, 300 wppm,
350 wppm, 400 wppm, 450 wppm, 500 wppm based on the total weight of
hydroxyl-functional polymer. Suitable upper limits for the amount
of tetracarboxylic acid dianhydride according to the present
invention are 50,000 wppm, 40,000 wppm, 30,000 wppm, 25,000 wppm,
20,000 wppm, 15,000 wppm, 10,000 wppm, 8,000 wppm, 7,000 wppm,
6,000 wppm, 5,000 wppm, 4,000 wppm, 3,000 wppm, 2,500 wppm, 2,000
wppm, 1,800 wppm, 1,700 wppm, 1,600 wppm, 1,500 wppm, 1,400 wppm,
1,300 wppm, 1,200 wppm, 1,100 wppm, 1,000 wppm based on the total
weight of the hydroxyl-functional polymer. At high crosslinker
levels for example at least 1,000 wppm, or at least 1,500 wppm, or
at least 2,000 wppm, or at least 2,500 wppm, or at least 3,000
wppm, or at least 4,000 wppm based on the total weight of the
hydroxyl-functional polymer the dissolution rate in water of the
reversibly crosslinked hydroxyl-functional water-soluble polymer
according to the present invention under neutral conditions may be
low.
[0043] In embodiments wherein the above-described high levels of
crosslinkers are used the particulate polymeric material withstands
dissolution under neutral condition but dissolves more rapidly if
the pH of the aqueous system changes to acidic or basic conditions.
This allows for a pH control of the dissolution rate of the
reversibly crosslinked polymer particles according to the present
invention in aqueous systems.
[0044] As mentioned above one advantage of the present invention is
that the method is very effective under mild reaction conditions
even without the use of any catalysts but catalysts may of course
be used, if appropriate. Consequently, the amount of catalysts can
vary within wide ranges. Suitable amounts of catalysts are 0.001 to
100 mol %, preferably 0.1 to 10 mol %, more preferred 0.5 to 5 mol
% based on the total moles of anhydride groups. Suitable catalysts
may be selected from metal alkoxides, metal carboxylates, Bronsted
acids and Lewis bases. For example imidazole may be used as
catalyst.
[0045] According to one embodiment of the present invention the
particulate water-soluble hydroxyl-functional polymer may be
treated with a liquid phase by suspending the polymer in the liquid
phase thereby forming a particulate reversibly crosslinked
polymeric material. Subsequently, the particulate reversibly
crosslinked polymeric material is separated from the liquid phase.
Suitable separation methods are all solid-liquid separation methods
known to a person skilled in the art. Examples are filtration,
sedimentation, centrifugation and evaporation. The recovered
particulate polymeric material may be washed and dried.
[0046] Alternative the particulate water-soluble
hydroxyl-functional polymer may be agitated in a high-shear mixer
for example horizontal ploughshare mixer or in a fluidized bed and
then treated with the above described aqueous phase by spraying the
aqueous phase onto the polymeric particles. The above-obtained
treated polymer particles may be subsequently washed and dried.
[0047] The present invention will now be described in more details
with reference to the following examples.
Following Materials were Used:
[0048] Pyromellitic acid anhydride (97%) was obtained from
Aldrich.
[0049] 1,2,3,4-Butanetetracarboxylic acid (99%) was purchased from
Aldrich.
[0050] Ethylenediaminetetraacetic acid dianhydride (98%) was
obtained from TCA America.
[0051] 1,2,3,4-Cyclopentanetetracarboxylic acid (90%) was purchased
from Aldrich.
[0052] Acetic anhydride (99.4%) was obtained from Fischer
Scientific.
[0053] All materials were used as received from commercial
sources.
Measuring Methods:
[0054] The dissolution behavior was evaluated in a Brabender
hydration apparatus as described below:
Equipment:
[0055] Brabender Visco-Corder.RTM. Model VC-3/A, fully recording,
stepless variable SCR speed control, with rpm display up to 200
rpm, 115 VAC, 60 Hz (Brabender Instruments Inc., South Hackensack,
N.J., USA), equipped with a stainless steel sensor paddle of
4.125'' (10.5 cm) total length, having two vertical rectangular
wings of 1'' (2.5 cm) width and 1.625'' (4 cm) height, a jacketed
sample bowl for use with heat transfer coil assembly, a 250 ml
stainless steel beaker, a circulating water bath and a pH meter
with standard calomel reference electrode and pH electrode.
Procedure:
[0056] The stainless steel beaker is centered in the jacketed
sample bowl. The space between the jacketed sample bowl and beaker
is filled with water. The beaker is charged with 200 ml of solvent
(either distilled water or any buffered aqueous solution, as the
case may be). The viscometer is turned on and the paddle is allowed
to stir the solvent at 200 rpm. The solvent is allowed to
equilibrate at 25.0.+-.0.2.degree. C. A pre-weighed sample of the
polymer is added to the solvent while stirring. The polymer is
added slowly to avoid lumping, but in less than one minute. The
chart recorder is turned on when the polymer is added (time=0). The
viscometer is allowed to run until the viscosity deflection reaches
a constant value (C.sub.max).
Example 1
Preparation of 1,2,3,4-butanetetracarboxylic acid dianhydride
(BTCA-DA)
[0057] [Follows the procedure of. Yang, C. Q.; X. J. Appl. Polym.
Sci. 1998, 70, 2711-2718.]
[0058] A 100 ml round-bottom flask with thermometer attached was
charged with stirbar, 1,2,3,4-butanetetracarboxylic acid (BTCA,
29.024 g, 124 mmol) and acetic anhydride (26.454 g, 259 mmol, 2.1
eq.) The flask was attached to a Schlenk line and the air was
replaced by nitrogen. The mixture was heated to mild reflux for 3.5
h, allowed to cool to 31.degree. C., and then unsealed and filtered
through a medium glass frit with vacuum assistance, washed with
ethyl acetate (50 ml) followed by hexane (20 ml). The sample was
kept under vacuum overnight at 30.degree. C. Yield: 23.84 g fine,
white powder (97%), M.P. 264.88.degree. C. by differential scanning
calorimetry (DSC).
Example 2
Treatment of Hydroxyethyl Cellulose with BTCA-DA
[0059] Hydroxyethyl cellulose having an ethylene oxide molar
substitution level (EOMS) of 1.586 and a viscosity of 7300 cP
(measured at 1% in distilled water at 25.degree. C. using spindle 2
and a stir speed of 6 rpm) (10.05 g) was slurried in 100 ml of a
mixture of acetone and distilled water (90:10 v:v), then were added
BTCA-DA (from Example 1, 0.4276 g) and imidazole (0.2055 g) for 3 h
at ambient temperature. The mixture was then filtered and washed
three times with 100 ml acetone/water (90:10 v:v), allowed to dry
in air and then dried overnight under vacuum at 50.degree. C. A
portion of the sample (1.9 g) which had been ground in a mortar and
pestle and passed through a 30 mesh sieve was added to 200 ml of an
aqueous buffered solution at pH 7.2 at 25.degree. C. in a Bradender
hydration apparatus. The solid did not increase the viscosity of
the slurry over the course of 1 h and sank to the bottom of the jar
when agitation was stopped.
Comparative Example 1
Treatment of Hydroxyethyl Cellulose with BTCA
[0060] The same polymer used in Example 2 (10.14 g) was slurried in
100 ml of a mixture of acetone and distilled water (90:10 v:v,
0.8293 g/ml), then were added BTCA (0.5066 g) and imidazole (0.2040
g) for 3 h at ambient temperature. Isolation and purification of
the product was done in a manner similar to that of Example 2. When
1.9 g of this sample (having passed through 30 mesh sieve) were
added to 200 ml pH 7.2 buffered solution at 25.degree. C. in a
Brabender hydration apparatus, the mixture rapidly built viscosity,
approaching 50% of its maximum within 7 min. Several large gels
were observed in the mixture.
Example 3
[0061] The same polymer used in Example 2 (10 g) was slurried in
100 ml of a mixture of acetone and distilled water (90:10 v:v). To
this was then added 1 ml of a freshly-prepared solution of 100 mg
of BTCA-DA in 20 g acetone/water (90:10 v:v). The mixture was
stirred at room temperature for 3 h, followed by filtration,
washing, drying, and sieving as in Example 2. In a hydration
experiment at pH 7.2 viscosity rose slowly and reached 100 (rel.
units) after 37 min.
Comparative Example 2
[0062] The conditions of Example 3 were repeated except no BTCA-DA
solution was is added. In a hydration experiment at pH 7.2,
viscosity rose rapidly and reached 970 (rel. units) after 40
min.
Example 4
[0063] The conditions of Example 3 were repeated except 0.5 ml of
BTCA-DA solution were added. In a hydration experiment at pH 7.2,
viscosity rose rapidly and reached 738 (rel. units) after 40
min.
Example 5
[0064] The conditions of Example 3 were repeated except 0.6 ml of
BTCA-DA solution were added. In a hydration experiment at pH 7.2,
viscosity rose at a moderate rate and reached 380 (rel. units)
after 40 min.
Example 6
[0065] The conditions of Example 3 were repeated except 0.75 ml of
BTCA-DA solution were added. In a hydration experiment at pH 7.2,
viscosity rose at a moderate rate and reached 255 (rel. units)
after 40 min.
[0066] The evolution of viscosity over time can be seen for
Examples 3-6 and Comparative Example 2 in FIG. 1.
Comparative Example 3
[0067] To a slurry of the same hydroxyethyl cellulose used in
Example 2 (10 g) in 100 ml acetone/water (90:10 v:v) were added 2.5
ml of a solution of 0.1033 g of pyromellitic acid anhydride
(1,2,4,5-benzenetetracarboxylic acid dianhydride) and the resulting
slurry was stirred for 3 h at room temperature. The product was
recovered and isolated as in Example 2. The behavior in a hydration
experiment at pH 7.2 was indistinguishable from that described in
Comparative Example 2.
Example 7
Preparation of 1,2,3,4-cyclopentanetetracarboxylic acid
dianhydride
[0068] 10 g of cis,cis,cis,cis-1,2,3,4-Cyclopentanetetracarboxylic
acid (10 g, 41 mmol) and stirbar were placed in a two-arm
round-bottom flask to which was attached a reflux condenser. Acetic
anhydride (8.894 g, 87 mmol, 2.1 eq.) was added via syringe.
Nitrogen was allowed to flow through a side arm for about 30 min.
Then a thermometer was attached to the side arm and the reflux was
started. After 3 h of is refluxing, the reaction mixture was
allowed to cool. Product was isolated by filtration through a
medium frit and washing with 25 ml of ethyl acetate and 20 ml of
hexane. Product was dried in a vacuum oven at 50.degree. C.
overnight. Yield: 8.16 g (95%), M. P.=213.8.degree. C.
Example 8
[0069] To a slurry of the same hydroxyethyl cellulose used in
Example 2 (10 g) in 100 ml acetone/water (90:10 v:v) was added 1 ml
of a freshly-prepared solution of 0.005 g of
1,2,3,4-cyclopentanetetracarboxylic acid dianhydride in
dimethylsulfoxide (DMSO, 10 g) and the resulting slurry was stirred
for 3 h at room temperature. The product was recovered and isolated
as in Example 2. In a hydration experiment at pH 7.2, viscosity
rose slowly and reached 140 (rel. units) after 38 min.
Example 9
[0070] To a slurry of the same hydroxyethyl cellulose used in
Example 2 (10 g) in 100 ml acetone/water (90:10 v:v) were added 1.5
ml of a freshly-prepared solution of 0.1031 g of
ethylenediaminetetracarboxylic acid dianhydride (EDTA-DA) in DMSO
(20 g) and the resulting slurry was stirred for 3 h at room
temperature. The product was recovered and isolated as in Example
2. In a hydration experiment at pH 7.2, viscosity rose slowly and
reached 100 (rel. units) after 42 min.
Example 10
[0071] The conditions of Example 9 were repeated except 1 ml of a
solution of EDTA-DA (0.1050 g) in DMSO (20 g) was added. In a
hydration experiment at pH 7.2, viscosity rose at a moderate pace
and reached 380 (rel. units) after 45 min.
Example 11
[0072] The conditions of Example 9 were repeated except 0.8 ml of a
solution of EDTA-DA (0.1040 g) in DMSO (20 g) were added. In a
hydration experiment at pH 7.2, viscosity rose rapidly and reached
740 (rel. units) after 40 min.
[0073] The evolution of viscosity over time can be seen for
Examples 9 to 11 and Comparative Example 2 in FIG. 2.
* * * * *